In many engines with fuel injection systems, it is desirable to supply liquid fuel to the fuel injector or injectors from a fuel pump which continuously delivers a flow rate of liquid fuel sufficient to supply the maximum fuel demand of the engine and hence, under engine operating conditions wherein the engine has a lesser fuel demand, there is an excess of fuel being supplied from the fuel pump. This is especially true when the engine is idling and has an extremely low fuel demand while the fuel pump is still delivering a high flow rate of fuel.
In such systems, a bypass regulator is utilized to provide a bypass fuel flow path downstream of the pump outlet through which excess fuel delivered from the fuel pump is returned to the fuel tank. The fuel pressure regulator may be located within the fuel tank immediately downstream of the fuel pump outlet to bypass excess fuel delivered from the fuel pump directly into the fuel tank. The fuel pressure regulator may also be located downstream of the engine fuel rail or injectors to bypass excess fuel to the fuel tank through a fuel return line. In this way, the pump can be continuously operated to maintain a high rate of fuel output so as to be able to accommodate a rapidly increasing demand for fuel at the engine.
Some previous fuel pressure regulators have used a flexible diaphragm spring biased to close a bypass passage. The diaphragm is responsive to an increase in fuel pressure acting thereon and when displaced, permits the fuel to flow through the bypass passage to be returned to the fuel tank. Although satisfactory in performance, and beneficial for the ability to accommodate thermally expanding or excess fuel, these fuel pressure regulators have a relatively slow response time causing undesirable fuel pressure pulsations which can affect the performance of the engine and can generate undesirable levels of noise in the fuel system. Further, due to the increased force per unit of displacement of the spring biasing the diaphragm, these regulators inherently produce an outlet fuel pressure delivered to the engine which decreases with increasing flow rate of fuel delivered to the engine. In some applications, it is desirable to provide fuel at a substantially constant pressure to the fuel injectors regardless of the flow rate of fuel delivered or at a pressure which increases with an increasing flow rate of output fuel delivered to the engine. Thus, it is desirable to have a highly responsive fuel pressure regulator which is versatile and may be easily calibrated to provide constant or increasing fuel pressure with increasing flow rate of output fuel delivered to the fuel injectors of the engine.